The present invention relates to Tonneau Covers, particularly Tonneau Covers including a flexible cover and an apparatus for attaching the flexible cover to a cargo box of a pick up truck; the apparatus includes a flexible cover securing plate and securing plate engagement members cooperating to impart tension to the flexible cover when the flexible cover securing plate pivots into or is positioned in a closed position with respect to the securing plate engagement members; and, preferably a locking member or members preventing unauthorized detachment of the flexible cover securing plate from the securing plate engagement members.